Re: Tracking inside secondary former

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Mark Fergerson by way of Terry Fritz <twftesla-at-uswest-dot-net>" <mfergerson1-at-home-dot-com>

Michael Tandy wrote:

<snip>

> I would still be most interested in hearing the theoretical underpinings of
> how internal flashover and carbon tracking originate in the first place --
> the conditions and electrical dynamics that cause this phenomenon.  My
> electrical background is pretty modest and some enlightenment on this would
> help me and perhaps others.  Anyone?

  My rule-of-thumb SWAG is based on the fact that, generally speaking,
arcs like to take the shortest available path. And, if there are any
sharp conductive corners (like a less-than-perfect solder joint or the
pointy bits of a hex nut) on the inside of the form, and nothing but
smooth surfaces (like a nice toroid and a good ground) on the outside,
you'll get higher e-field intensities on the inside to start arcs with
in the first place.

  Once the arc starts it will rapidly heat the nearest material; the
core. Since the heat is very localized carbonization is inevitable.
Once a carbon track is started good external spark generation is
unlikely.

  OTOH that "generally speaking" above is mitigated by such things as
path heating and self-repulsion (writhing arcs).

  The above ignores form defects (holes, conductive inclusions, etc.),
uneven windings, and other possible causes of e-field inhomogeneties.

  Mark L. Fergerson